1. Field of the Invention
The present invention generally relates to a method of and apparatus for detecting a network failure, and particularly relates to a method of and an apparatus for detecting a failure of an optical network.
2. Description of the Related Art
Network traffic has been increasing at a rapid rate, and, also, there has been the emergence of services such as VoIP (Voice over Internet Protocol) that require real-time properties. Against this background, there is an urgent need for the provision of a transport network that achieves high capacity and flexible network control.
In order to provide such network, it is necessary to incorporate IP technology capable of flexible network control into a transport network. Organizations for standardization have been studying relevant network architectures and the detail of protocols.
The formulation of specifications for the GMPLS (generalized MPLS) signaling protocol has been underway where the GMPLS expands the structure of MPLS (multi-protocol label switching) by introducing structures developed for conventional router networks into a transport network. As shown in FIG. 1, a IP-based control plane 2 is introduced into a transport network 1 for the purpose of setting wavelength paths, SONET/SDH channels, etc., by use of signaling.
Such a network in which the IP-based control plane 2 is utilized for the existing transport plane 1 is useful for the purpose of establishing a future core network, and its further development is expected.
When recovery from failure needs to be made in the network as shown in FIG. 1, a backup path is generally provided at the time a path for current use is provided in the transport plane 1, or a backup path is provided based on the routing computation performed at the time of failure occurrence. In recovering from failure, a point of failure is identified, and control for recovering from the failure is performed.
Technologies for failure identification include the following. A first one is a method of identifying a failure point based on ITU-T recommendation G.709. This method transmits a failure notification message by use of hardware, and allows exchanges of the failure notification message in each optical layer, thereby achieving high-speed failure detection and identification. For example, if an optical fiber is severed, signals for failure notification travel between layers for optical transmission such as an OMS (optical multiplexing section) and an Och (optical channel). This makes it possible to identify which portion of which layer suffered a failure.
A second one is a method based on the LMP (Link Management Protocol) of the IETF (Internet Engineering Task Force) standard. The LMP provides a function to localize a failure point in an optical network. When a failure is detected in the LMP, an inquiring message is sent upstream, and a response is sent back from upstream to identify a failure point.
Moreover, technologies for detecting network failure include those described in Patent Documents 1-3.
Patent Document 1 teaches identifying a main cause reported from a transmission apparatus being monitored in an integrated network management system, which is comprised of a plurality of sub-network management systems and a network management system for consolidating these systems.
Patent Document 2 teaches carrying out signaling via a control network and establishing/canceling connections through a transmission network when communication connections are to be established/canceled.
Patent Document 3 teaches a control unit of an exchange that is connected to a network control apparatus through an exchange control network, wherein the control unit responds to a request for information transfer given from the network control apparatus by detecting unused timeslots on a highway connected to the transfer destination and by transmitting maintenance information through the unused timeslots.                [Patent Document 1] Japanese Patent Application Publication No. 11-205318        [Patent Document 2] Japanese Patent Application Publication No. 2003-508971        [Patent Document 3] Japanese Patent Application Publication No. 2003-92626        
The first method based on the ITU-T recommendation G.709 needs optical-to-electrical conversion at each node of the transport plane 1. Because of this limitation, this method cannot be applied to a network in which all the paths are cross-connected through optical signals. In such a network, path switch is possible for recovery from failure only between edge nodes where optical-to-electrical conversion is performed. This method of recovering from failure cannot be applied if relay nodes that do not perform optical-to-electrical conversion are required to set a detour route according to the method.
The second method based on the LMP requires messages to be exchanged both ways with an adjacent node, which results in a lengthy delay. Further, this method cannot cope with a node failure, i.e., cannot detect a node failure.
In the technology described in Patent Document 1, no control plane is present, and the integrated network management system identifies a main cause reported by a transmission apparatus that is being monitored. In the technology described in Patent Document 2, a transfer network and a control network are separated, but there is no mention of identifying a failure point in the transmission network. Patent Document 3 inserts maintenance information into unused timeslots of a transmission path for transmission. This is different from identifying a failure location by transmitting a failure information message on the control plane.
Accordingly, there is a need for a method of and an apparatus for detecting a network failure that can detect a node failure with a short delay of failure detection in a network where cross-connect is provided through optical signals.